Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
979 FXUS63 KARX 271820 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 120 PM CDT Thu Jun 27 2024 .KEY MESSAGES... - Storm Chances Return Tonight, Lingering Through Friday. A Widespread 0.5" to 1.0" of Rainfall Is Expected. - Slightly Below Normal Temperatures This Weekend. - Subsequent Storm Chances Monday, Lasting Into Tuesday. && .DISCUSSION... Issued at 325 AM CDT Thu Jun 27 2024 Rain & Storm Chances: Initial precipitation chances reach our western peripheral counties in southeast Minnesota and northeast Iowa tonight ahead an upper level trough seen over the northwest CONUS on GOES water vapor imagery early this morning. These initial precipitation chances are expected to remain along our west though as the ridge lingers locally. Eventually, the progressive pattern and veering of the moist low level jet increases precipitation chances through the overnight hours locally. As a result of these passing moisture lobes, have quickened initial onset near 27.21Z only in these western counties. As the synoptic low wobbles and phases east, precipitation and storm potential persists through Friday into early Saturday morning. Rainfall Amounts Through Friday: Higher rainfall amounts overnight are expected to remain along our northwestern periphery aligned with the nose of the heightened low level moisture gradient, northerly lifting low level trough, and associated frontogenetical bands. HREF confidence suggests a mean of 0.25" to 0.5" to a maximum near 1" along our periphery during this time. Through Friday, as a low level trough advects southwest-northeast oriented frontogenesis bands within the heightened low level moisture transport, narrow corridors of ~0.75" mean rainfall amounts spread east through the forecast area. In summary, highest confidence for a widespread 0.5" to 1.0" across the forecast area by Saturday morning. Local Severe Threat: Quite a conditional severe storm threat at the current forecast hour as the main wave passage is expected to remain outside of peak diurnal heating and associated building instability. Therefore, current confidence places heavy rain as the primary hazard. With a quick storm motion, ~30kts, the threat for damaging winds also cannot be ruled out in this scenario. However, quickening of the synoptic pattern would present more of a severe storm threat scenario locally. As a result, the quickest high resolution model solutions show a line of storms building Friday evening and progressing through the forecast area. Given the ongoing precipitation and small storm potential, building sufficient instability remains questionable. Temperatures This Weekend: Slightly below normal temperatures on tap for the week as a cold frontal boundary shifts east across the Upper Mississippi River Valley Saturday morning. An amplified upper level ridge in its wake sustains these slightly below normal temperatures through Sunday. Long term global ensemble confidence suggests temperatures approximately 10 degrees below normal for the weekend. Subsequent Storm Chances Next Week: Long term global ensemble confidence suggests the amplified ridge exiting east into Monday, returning storm activity from west to east Monday into Tuesday. Similar to Friday, separate upper level synoptic troughs are resulting in main impacts remaining to the north and south of the local forecast area. The initial wave is expected to lift north through the Northern PLains through Monday, leaving an increased low level theta e axis draped across the local forecast area. Subsequent perturbations and low level troughs may perpetuate precipitation and storm potential through Tuesday. Spread in individual ensemble (EPS/GEFS) member low locations extends from the Southern Plains into central Saskatchewan and Manitoba. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 120 PM CDT Thu Jun 27 2024 VFR conditions have prevailed into this early afternoon, with current satellite imagery showing clouds increasing across the area. Main TAF concerns will come with increasing shower chances across the area this evening into Friday. Some of the model guidance suggests potential for MVFR ceilings, but there is a bit of variability on timing. With MVFR probabilities from guidance increasing (~40-70%) for Friday morning have trended that way and will continue to monitor for any adjustments needed. South/southeast winds increase late tonight into Friday with some gusts 20-25+ kts possible. && .HYDROLOGY... Issued at 401 AM CDT Thu Jun 27 2024 While rivers continue to fall below flood stage, most of this water is still on route to the Mississippi River. As a result, the Mississippi River is expected to keep rising through the next 3 to 5 days depending on location and routing of tributary rivers. While official forecasts from the River Forecast Center do take into consideration all of the water that has already fallen and is on its way into the Mississippi River, it only takes the next 24-48 hours of forecast precipitation. The next chance of precipitation returns late tonight lasting through Friday. While widespread amounts of 0.5" to 1.0" are not expected to immediately or substantially affect ongoing flooding concerns, an additional widespread 1" to 2" of rainfall upstream will prolong residence of elevated river levels. As a result, the Mississippi River levels may initially slightly decrease before increasing again as the additional rainfall flows downstream this weekend into next week. Elevated rivers with ongoing minor to moderate flood stages from Lake City through Guttenberg are expected to persist beyond the next 7 to 10 days. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...JAR AVIATION...EMS HYDROLOGY...JAR